An image forming apparatus has a printer that forms a visible image according to image data on a sheet. As the image forming apparatus, a MFP (Multi-Functional Peripheral) having a scanner for acquiring characters, illustrations, or photographs on an object to be read as intensity of light and generating image data corresponding to the intensity in addition to the printer is widely used. An electrophotographic printer is widely used as the printer of the image forming apparatus. Such a printer has a plurality of light sources for emitting laser beams to form an electrostatic latent image.
Such an image forming apparatus performs an image quality maintaining control for keeping an image density constant regardless of environmental conditions. The image quality maintaining control is a control for adjusting image densities of all colors including yellow (Y), cyan (C), magenta (M), and black (K) to respective target values of YMCK. The adjustment is performed by regulating laser power, charging/developing bias high voltage output and primary transfer high voltage output of each of a laser optical system, a developing device and a transfer belt which are used for image formation. In the image quality maintaining control, if the image density cannot be adjusted to the target value, it is determined that an abnormality occurs, and the abnormality is notified to a user through a message such as an error display on a display section of an operation panel of the image forming apparatus.
A toner adhesion sensor for detecting the toner density is used in the image quality maintaining control. Specifically, a dedicated pattern for each color of YMCK is printed on a surface of a transfer belt, and the dedicated pattern is read by the toner adhesion sensor to detect the toner density.
Although the abnormality in the density is notified through detection of an image defect in the image quality maintaining control, it is not possible to determine whether the abnormality in the density is caused by failure in any one of the laser optical system, the developing device, and the transfer belt which are used for image formation, in other words, it is not possible to specify a failure occurrence location. Therefore, much time is required to specify the failure occurrence location at the time of maintenance.
As a result, there is a case in which the image forming apparatus has an overcurrent detection function (LD breakage detection), a voltage leakage detection function for any one of the laser power, the charging high voltage output, and the primary transfer high voltage output as failure detection functions on hardware of each of the laser optical system, the developing device, and the transfer belt. However, this is an additional function, resulting in an increase in cost.